1. Field of the Invention
The present invention relates to a filtering device having a filter washing capability, and more specifically to a filtering device having the self-cleaning function and the alga or seaweed adhesive preventing function during the rotation of the drum.
2. Description of the Related Art
There have been proposed various filtering devices such as a filtering device in which washing water is jetted against a filter layer to wash the filtering material, another device in which air is compressed and fed together with reverse washing water from a bottom of a filter bed and is stirred to wash the filter material, and the like. However, the conventional devices suffer from defects that the filter material cannot sufficiently be washed, it takes a large amount of washing water and a long time to wash the filter material, and the filtering mechanism is complicated and become large in size.
Accordingly, in view of the foregoing defects, the present inventors have proposed a filtering device in which the filter material may be well washed, the filtering mechanism may be simplified and may become small in size, and the filtering capability is enhanced (Japanese Examined Patent Publication No. 61-41246, British Patent Publication No. 2141039A and U.S. Pat. No. 4,556,487).
As shown in FIG. 11, in this device, a filter layer 101 composed of granular filter material and a space 102 are formed in the interior in the vertical direction. The device includes a rotatable horizontal drum 103, a crude water introducing/dirty water discharging first water flow pipe 105 which passes a central portion of the horizontal drum 103 in the axial direct on from the outside of the horizontal drum 103 and which has a crude water introducing/dirty water discharging first water flow portion 104 located in the space 102, and a filtered water introducing/washing water discharging second water flow pipe 107 which passes the central portion of the horizontal drum 103 in the axial direction from the outside of the horizontal drum 103 and which has a filtered water introducing/washing water discharge second water flow portion 106 located within the filter layer 101.
The above-described first and second water flow pipes 105 and 107 are securely fixed to a support frame 108 so as not to rotate when the horizontal drum 103 rotates. These pipes extend to the interior of the drum 103 and pass through the central portion of the drum 103 in the diametrically opposite direction. The drum 103 is driven by a drive force of the motor (not shown) around the stationary shafts of the parts of the first water flow pipe 105 and the second water flow pipe 107 extending along a rotary axis. Also, the parts of the first water flow pipe 105 and the second water flow pipe 107 extending along the rotary axis are integrally formed with each other by using a single pipe member. The midway portion of the pipe member is partitioned by a partitioning member 109 to form the first water flow pipe 105 and the second water flow pipe 107. In the second water flow portion 106 of the second water flow pipe 107, a portion 111 where second water flow ports 110 are formed is surrounded by a filter mesh 112, a sliding contact member 113 which is brought into sliding contact with the inner surface of the filter mesh 112 when the filter material is washed are provided between the filter mesh 112 and the portion 111. The sliding contact member 113 is formed by a helical linear member wound around a portion 111 where the second water flow ports 110 are formed. The second water flow portion 106, the filter mesh 112 and the sliding contact member 113 form a strainer S. An agitating member 114 for assisting the movement of the granular filter material when the drum 103 is rotated is provided on the inner circumferential surface of the horizontal drum 103.
Also, as shown in Japanese Patent Application Laid-Open No. Hei 7-171313, there is another approach in which the filter space portion is formed by dividing the interior of a rotary member into three in the vertical direction by partitioning plates having water flow apertures, and the granular filter material is provided to be movable within the filter space portion in accordance with the rotation of the rotary member. However, this simply means the device in which the interior of the rotary member is divided into three in the vertical direction by the partitioning plates having the water flow apertures. This does not mean the intent to positively utilize the function of the strainer.
Turning back to the conventional device shown in FIG. 11, since the area of the strainer may only be formed to the limited portion, the area for the filtering function is small and its efficiency is low. In addition, it takes a long time to perform the opposite washing. This leads to the consumption of a large amount of washing water. Also, in the fixed strainer, a friction with the granular filter material is increased. However, on the other hand, its damage or flaw is remarkable. This means the difficulty in maintenance work such as replacement.